1. Field of the Invention
The present invention relates to a communication apparatus configured to execute a facsimile communication via an Internet Protocol (IP) network, and a control method thereof.
2. Description of the Related Art
Recently, a broadband line, such as Asymmetric Digital Subscriber Line (ADSL) or Fiber to the Home (FFTH), has remarkably become widespread. To make the best use of a high-speed transmission property of the broadband line, an Internet Protocol (IP) telephone service for transmitting a speech signal with IP packets has increased rapidly.
According to the IP telephone service, speech data is transmitted and received between terminals having IP addresses with Transmission Control Protocol/Internet Protocol (TCP/IP) or User Datagram Protocol/Internet Protocol (UDP/IP) layer. Protocols include Voice over IP (VoIP), such as ITU-T Recommendation H.323. Accordingly, a conversion process from a telephone number to an IP address is required. Currently, the conversion from the telephone number to the IP address is typically performed with a Session Initiation Protocol (SIP) proxy server (RFC2543).
As for the IP telephone communication using SIP, when a telephone number is input at a caller terminal, a session request message that includes a transmission destination telephone number is transmitted to the SIP proxy server. The SIP proxy server, which has received the session request message, obtains an IP address of a callee terminal by performing a necessary process, such as searching a Domain Name System (DNS) server (RFC1035). Accordingly, the SIP proxy server stands proxy for an initial connection process between the caller terminal and the callee terminal. A response message to the session request message is transmitted from the caller terminal. However, these messages are both text streams expressed with text (i.e., character code).
The main part of the SIP message is written in a format which is similar to, for example, a header description format of e-mail, such as “property: value”. Then, a process function (i.e., communication function) related to own device's media stream can be written in a format compliant with Session Description Protocol (SDP) (RFC2327) to identify mutual functions of the terminals. Listed below is an example of SDP declaration (proposal) of the caller terminal described in Appendix of RFC2543 “B. 1 Configuring Media Streams”.    v=0    o=alice 2890844526 2890844526 IN IP4 host.anywhere.com    c=IN IP4 host.anywhere.com    m=audio 49170 RTP/AVP 0    a=rtpmap: 0 PCMU/8000    m=video 51372 RTP/AVP 31    a=rtpmap: 31 H261/90000    m=video 53000 RTP/AVP 32    a=rtpmap: 32 MPV/90000
As described above, SDP includes “=” positioned after one character mnemonic (v, o, c, m . . . ), followed by text-expressed values separated by slashes and spaces. Particularly, mnemonic “m” can express types of media stream to be processed by a terminal, such as audio and video. Also, mnemonic “v” is used to identify a protocol version, mnemonic “o” is used to identify an initiator or owner of the session (or message), and mnemonic “c” is used to describe various connection information.
On the other hand, facsimile apparatuses, which can easily transmit and receive image data, have been used before the IP network, such as the Internet, became popular. Transmission of image data to a destination with a facsimile apparatus is extremely simple just by specifying a telephone number. Yet, facsimile apparatuses are widely used even today where images can be transmitted from personal computers (PCs) or cellular phone terminals via e-mail.
Currently, as a procedure to utilize a facsimile procedure for communication over the IP network, a so-called real-time Internet facsimile procedure, described in ITU-T Recommendation T.38, is known. ITU-T Recommendation T.38 defines a procedure which is defined by ITU-T Recommendation T.30 as it is over the IP network, on the premise that the facsimile communication protocol is to be used on a public switched telephone network (PSTN).
As a procedure to avoid data error occurrence determined in ITU-T Recommendation T.30, there is known a communication using Error Correction Mode (ECM). The ECM is defined on the premise that a data error occurs in a communication network, and is valid on the public switched telephone network. However, in the case where an Internet facsimile using the IP network is selected, especially where TCP/IP having an error correction function is selected, the data error is checked for redundantly twice. Thus, a problem arises in that the data transmission efficiency may be lowered as a result of checking for data error multiple times.
In regard to such a problem, one can consider a facsimile communication method for omitting the ECM procedure and defining its own communication mode.
For example, as discussed in Japanese Patent Application Laid-Open No. 2001-292267, in a non-standard procedure communication for performing data communication at the same channel as a call control channel, a capability negotiation is performed with a destination device using a call control message via the call control channel. In this capability negotiation, a sending device notifies the destination device that the sending device supports data transfer omitting the ECM procedure.
However, in the case of the communication discussed in Japanese Patent Application Laid-Open No. 2001-292267, notification/non-notification of the ECM procedure is performed in the non-standard procedure communication. Accordingly, it lacks in communication versatility for different manufacturers' apparatuses.